Omnidirectional high sensitivity hydrophone

ABSTRACT

A spherical-shell transducer, formed of two hemispherical shells bonded together, has inner and outer metal films radially aligned in quadrature to define eight discrete sections sensitive to impinging, acoustic energy to generate representative signals. Connecting the sections in series and encasing them in a viscous, dielectric substance, contained in a shielded, flexible boot, provides a broadband, highly sensitive hydrophone. Filling the spherical shell with the viscous dielectric and including a vent allowing a fluid communication between its interior and exterior render the hydrophone insensitive to ambient pressure variations. A preamplifier, optionally included, ensures the transfer of the representative signals to remote circuitry via an interconnected coaxial cable.

United States Patent [191 Holloway [451 Apr. 16, 1974 OMNIIDIRECTIONAL HIGH SENSITIVITY HYDROPHONE [75] Inventor: Jack W. Holloway, Chula Vista,

Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, D.C.

22 Filed: Feb. 16, 1971 21 Appl. No.: 115,427

[52] US. Cl. 340/10, 340/13 R Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Harold Tudor Attorney, Agent, or FirmRichard S. Sciascia; Ervin F. Johnson; Thomas G. Keough [5 7] ABSTRACT A spherical-shell transducer, formed of two hemispherical shells bonded together, has inner and outer metal films radially aligned in quadrature to define eight discrete sectio ns sensitive to impinging, acoustic energy to generate representative signals. Connecting the sections in series and encasing them in a viscous, dielectric substance, contained in a shielded, flexible boot, provides a broadband, highly sensitive hydrophone. Filling the spherical shell with the viscous dielectric and including a vent allowing a fluid communication between its interior and exterior render the hydrophone insensitive to ambient pressure variations. A preamplifier, optionally included, ensures the transfer of the representative signals to remote circuitry via an interconnected coaxial cable.

7 Claims, 5 Drawing Figures [51] Int. Cl. H04b 13/00 [58] Field of Search 340/8, l0, 12, 13

[56] References Clted UNITED STATES PATENTS 3,221,296 11/1965 Milne 340/10 3,230,504 H1966 Horan et al..... 340/10 3,328,752 6/1967 Sims 340/8 LF 2,417,830 3/1947 Keller 340/8 LF 3,564,49l 2/197] Granfords et al. 340/10 2,966,656 12/1960 Bigbie et al 340/10 WWW 16 m4 3.805226 SHEEI 1 OF 2 INVENTOR. JACK W. HOLLOWAY THOMAS GLENN KEOUGH ERVIN F. JOHNSTON ATTORNEYS PMHEWR 16 1914 3305228 SHEET 2 BF 2 INVENTOR. JACK W. HOLLOWAY F565 BY THOMAS GLENN KEOUGH ERVIN F. JOHNSTON ATTORNEYS OMNIDIIRECTIONAL HIGH SENSITIVITY HYDROPHONE STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufac tured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Hydrophones for monitoring ambient, marine, acoustic patterns must have the capability of being deployed at widely varying depths to reliably, acoustically portray what has been monitored. At extreme depths, those approaching 20,000 feet where ambient pressures of nearly 10,000 psi are encountered, air filled transducers are virtually useless since the sealing arrangements collectively failed. While certain oil-filled hydrophones hold up under the severe surrounding pressures, their asymmetrical configuration gives rise to internal, cross-coupling modes and the creation of nonuniform, directional listening beam patterns. Orienting these asymmetrically-shaped hydrophones differently on successive occasions provides inconsistent and erroneous acoustic images of the same area. All the conventional hydrophones fail to provide a substantially linear response over a kilohertz bandwidth. One notable attempt to eliminate the above enumerated difficulties called for including a spherical, shellshaped, piezoelectric element having its internal and external surfaces coated with a metallic conductor. Tangentially polarizing the spherical shell, and joining conductors to the internal and external surfaces did give it an omnidirectional capability and a linear response over the 10 kilohertz bandwidth. However, the sensitivity of this element left much to be desired and was totally inadequate for monitoring the weak, ambient, acoustic patterns.

SUMMARY OF THE INVENTION The present invention is directed to providing a hydrophone having a spherically-shaped shell of material responsive to impinging, acoustic energy to provide representative signals. A plurality of discrete, metallicfilm-coated areas, electrically insulated from one another on the internal surface of the spherically shaped shell is opposed by a plurality of radially aligned, metallic films disposed on the external surface of the spherically shaped shell. A plurality of conductors, reaching between adjacent metal films on the outside of the shell to adjacent metal-film areas on the inside of the shell, electrically connects, in series, the sandwiched area of the spherical shell creating a hydrophone highly sensitive to impinging, acoustic energy.

Therefore, a prime object of the invention is to provide a sensitive, omnidirectional hydrophone.

A further object of the invention is to provide a hydrophone insensitive to changing ambient pressures.

Yet another object is to provide a hydrophone insensitive to spurious, electrical, electromagnetic energy.

Still another object is to provide a hydrophone capable of presenting substantially identical operational characteristics when operating under extreme pressure variations.

These and other objects of the invention will become more readily apparent from the drawings when taken with the ensuing specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of the invention operationally deployed.

FIG. 2 is a cross-sectional view of the invention generally taken along lines 22 in FIG. ll.

FIG. 3 is a sectional view of the piezoelectric, spheri cal shell generally taken along lines 3-3 in FIG. 2.

FIG. 4 is a sectional view of the piezoelectric, spherical shell generally taken along lines 44 in FIG. 2.

FIG. 5 is a schematic representation of the electrical interconnection between sections of the spherical shell.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, an improved hydrophone 10 is suspended and operationally deployed in a water medium by a coaxial cable 111 reaching to remotely disposed, responsive circuitry. The cable terminates in a cone-shaped, rubber fitting l2 molded about and secured to the cables end in a sealed relationship, and cable leads extend through the rubber fitting and form cable terminal points llla, 11b, 11c, and Kid. A terminal board 13 is included to support the terminal points for electrical interconnection to following circuitry.

A metal sleeve 14 is molded into the rubber fitting and is shaped with a plurality of circumferentially running grooves 14a which aid in holding the metal sleeve in the rubber fitting. An axially aligned boot 15 formed of rubber, or a similar flexible material, is elastically fitted onto the metal sleeve and, when a bonding agent is included between them, a sealed interconnection is set up between the two elements.

At its opposite end, the rubber boot is provided with an access port 16 normally sealed closed by a sealed combination fitting 17 consisting of a tapped wall member receiving a correspondingly shaped, slotted plug. The slotted plug is removable to permit the passage of a fluid described below.

A copper-mesh sheath 1 .8 is bonded on the boots inner surfaces along its complete internal reaches and is of a relatively lightweight gauge to avoid damping or blocking the transmission of impinging, acoustic energy as it passes through the rubber boot. However, the mesh is sufficiently constructed to afford some degree of physical protection of the components contained within the boot while electrically shielding them from spurious, ambient, electromagnetic signals which foreseeably would produce false information signals. Interconnection to the coaxial cable's shield, or common lead, at terminal point 11a, via the sheaths terminal 18a, effectively grounds-out the unwanted signals.

For the magnitudes of the signals involved and the relatively linear response desired between 10 hertz and 10 K hertz, a preamplifier 20 was selected, a commercially available model 240B-2 rnan ufactui ed by Marine Resources, Incorporated, Electroinarine Sciences Division, located at 8762 Amigo Avenue in North Ridge, Calif. Its gain was found to be i 1 db. at the 1 kilohertz, and at the 10 hertz points and had an extreme variation between 10 hertz and 15 kilohertz, within i 2 db. Increasingly satisfactory operation of the improved hydrophone was ensured when it was noted that the gain stability of the selected preamplifier was within 1*: 1 db. over a temperature ranging from 32F. to 80F., and an ambient pressure range of between to 10,000 psi.

This preamplifier, disposed within the flexible rubber boot, is electrically joined to the terminal board by a pair of balanced outputs reaching to terminal points 11b and Me, as well as by a biasing connection reaching to the biasing terminal point 11d. Stable operation is further ensured by having the preamplifier sharing the common terminal 11a with the interconnection to sheath terminal 18a.

Via leads reaching from a pair of amplifier input points 20a and 20b, the preamplifier and cable are placed in electrical communication with a sphericalshell transducer having its own pair of outwardly reaching output terminals 30a and 3012 joined to the leads. The only other physical points of connection of the spherical-shell transducer to any of the aforedescribed structure are through a plurality of soft, acoustically decoupling, resilient spacers 31 bonded onto the outer shell of the transducer and the inner surface of the rubber boot. The resilient spacers hold the spherical-shell transducer away from the walls of the rubber boot and the preamplifier to prevent the selfgeneration of error signals should the hydrophone be accidentally bumped or jarred. Although there are shown only resilient spacers in one plane, it is obvious that all-around acoustic decoupling of the sphericalshell transducer from the rubber boot calls for there being additional resilient spacers reaching out in other planes.

Thusly arranged, the plug is removed from sealed combination fitting l7 and the entire interior of the rubber boot is filled with a viscous, delectric substance 2], such as oil, to remove all voids. Prior to its being placed in the hydrophone, the interior of the sphericalshell transducer also is filled with the viscous dielectric. After replacing the plug in the sealed combination fitting, ambient pressure variations have little, if any, effect on the hydrophone since its interior is filled completely with solid components and the noncompressible viscous dielectric.

The spherical-shell transducer is fabricated from a pair of commercially available hemispherical shells 32 and 33. in the present example, the shells are a molded lead-zirconate-titanate compound, having a composition marketed under the standard designation Type PZT-4. For the particular application in hand, shells having a one-eighth inch thickness and a two and onetenth inch outer diameter are internally and externally uniformly coated with a silver metalic film, it being fired-on to ensure a uniform distribution over the hemispherical shells. The shells are radially polarized, according to well known techniques, and when they are deformed by, for example, impinging acoustic energy, a representative signal is created across the two metal films.

Noting FIG. 3 and FIG. 4 to achieve the desired degree of sensitivity, the two hemispherical shells are modified by removing strips of the deposited film to create insulator strips 341 dividing separate electrically conductive surfaces 32a, 32b, 32c, and 32d on the outer surface of hemispherical shell 32, and electrically conductive surfaces 32e, 32f, 32g, and 32h on its internal surface. Similarly, hemispherical shell 33 has its internal and external conductive surfaces separated by insulator strips 34 to define electrically conductive surfaces 33a, 33b, 33c, and 33d, and electricallyconductive surfaces 33e, 33f, 33g, and 33h, internally and externally. Greater sensitivity is ensured by serially connecting an outer electrically conductive surface to its neighboring inner conductive surface using individual conductor leaves 35, reaching across insulator strips vacant of the metal film.

By serially connecting all the conductive surfaces in this manner, a plurality of serially connected transducer sections is created which feed their additive portions of signals representing impinging, acoustic energy to preamplifier 20. Since there is danger of between arcing or destroying adjacently disposed sections of a piezoelectric hemispherical shell if adjacent sections are oppositely polarized, the orientation of the conductor leaves permits serial interconnection and a transducer of increased sensitivity.

Looking, in particular, to FIG. 5 showing the schematical representation of the electrical interconnection, the sections of hemispherical shell 32 are serially connected by conductive surfaces 320 through 32h, joined by a separate conductor leaf 35 reaching between adjacent, outer conductive surfaces and inner conductive surfaces.

Identically, conductor leaves 35 join conductive surfaces 33a through 33h to serially connect the sections of hemispherical shell 33 and the sections of both hemispherical shells are connected in series by a single traversing conductor leaf 35a.

After the conductor leaves have been connected, as disclosed, the hemispherical shells are bonded together by a bonding agent having substantially the same strength, mass, etc., as the shell material. A satisfactory bonding agent having the desired characteristics is marketed under the trademark EPON VI by the Epoxy Hysol Division, Dexter Corporation, Pittsburg, Calif. 94565.

The bonding agent is layered to a thickness of approximately 1 /2 mills and, in addition to holding the hemispherical shell together, electrically insulates the conductive surfaces and conductor leaves from unwanted connections.

From this manner of mechanical and electrical connection, cross-coupling of dissimilarly-shaped transducer sections is eliminated since the aforedescribed spherical shell presents an identical acoustic energy receiving face in all directions. If a source of distant acoustic energy ensonifies the present invention at any direction from an identical range, the signals generated across the several sections, receiving the energy additively, produce a composite representative signal across transducer output terminals 30a and 30b.

A Helmholtz resonator unit 40 is mounted in the spherical shell to provide a dual function for improved hydrophone operations, those being, to provide an orifice 41 for allowing pressure equalization when the hydrophone is used at varying depths and, to provide a low frequency cutoff at 10 hertz. The particular resonator employed is dimensioned with respect to orifice diameter and overall length to achieve the 10 hertz cutoff and follows established Helmholtz resonator theory set out in the publications, Fundamentals of Acoustics by L. E. Kinsler and A. R. Frey, Chapt. 8, John Wiley & Sons, New York, 1950; or Vibration and Sound", 2nd Ed. by P. M. Morse, McGraw-Hill, N. Y., 1948.

The resonator is inserted through a hole bored in hemispherical shell 32 and is bonded in place by the bonding agent to preserve the integral nature of the spherical-shell transducer.

All the components exposed to the water medium are corrosion resistant and since the metal films and conductor are encased in the viscous dielectric, the entire hydrophone is immune from the adverse effects of the hostile marine environment.

The incompressible nature of the viscous dielectric filling the boot and spherical-shell transducer provides a pressure nonresponsive capability.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings, and, it is therefore understood that within the scope of the disclosed inventive concept, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A hydrophone comprising:

a pair of hemispherically shaped shells responsive to impinging acoustic energy to provide representative signals being bonded together to assume the configuration of a spherical shell;

a plurality of inner conductive means carried on the inner surface of each of said hemispherically shaped shells electrically insulated from one another;

a plurality of outer conductive means carried on the outer surface of each of said hemispherically shaped shells electrically insulated from one another and each radially aligned with a discrete said inner conductive means to sandwich discrete sections of said pair of hemispherically shaped shells therebetween, and

conductor means joining separate said inner conductive means to adjacent said outer conductive means to connect said sections of said pair of hemispherically shaped shells electrically in series ensuring uniform omnidirectional sensitivity to said impinging acoustic energy.

2. A hydrophone according to claim 1 further including:

a flexible boot encasing said spherical shell;

a viscous dielectric substance filling said flexible boot and the interior of said spherical shell for transmitting said impinging acoustic energy thereto, said spherical shell is additionally provided with a means permitting a fluid communication between its interior and the interior of said flexible boot rendering said hydrophone insensitive to ambient pressure variations; and

a metallic mesh sheath bonded onto and into said flexible boot for shielding said spherical shell from ambient electromagnetic interference.

3. A hydrophone according to claim 2 further including:

a preamplifier disposed in said flexible boot connected to said conductor means for amplifying and passing said representative signals to remote circuitry.

4. A hydrophone according to claim 3 further including:

a plurality of elastomers resiliently positioning said spherical shell in a spaced relationship from said flexible boot and said preamplifier preventing contact therebetween and the resultant generation of false signals.

5. A hydrophone according to claim 4 further including:

a coaxial cable reaching into said flexible boot connected to receive said representative signals and to pass them to remote circuitry.

6. A hydrophone according to claim 5 in which said inner conductive means and said outer conductive means are metal films deposited on the inner and outer surfaces of said pair of hemispherical shells.

7. A hydrophone according to claim 6 in which the inner conductive metal films define quadrature areas on each hemispherical shell and the outer conductive metal films define aligned quadrature areas creating eight said sections for serial interconnection creating increased omnidirectional sensitivity. 

1. A hydrophone comprising: a pair of hemispherically shaped shells responsive to impinging acoustic energy to provide representative signals being bonded together to assume the configuration of a spherical shell; a plurality of inner conductive means carried on the inner surface of each of said hemispherically shaped shells electrically insulated from one another; a plurality of outer conductive means carried on the outer surface of each of said hemispherically shaped shells electrically insulated from one another and each radially aligned with a discrete said inner conductive means to sandwich discrete sections of said pair of hemispherically shaped shells therebetween, and conductor means joining separate said inner conductive means to adjacent said outer conductive means to connect said sections of said pair of hemispherically shaped shells electrically in series ensuring uniform omnidirectional sensitivity to said impinging acoustic energy.
 2. A hydrophone according to claim 1 further including: a flexible boot encasing said spherical shell; a viscous dielectric substance filling said flexible boot and the interior of said spherical shell for transmitting said impinging acoustic energy thereto, said spherical shell is additionally provided with a means permitting a fluid communication between its interior and the interior of said flexible boot rendering said hydrophone insensitive to ambient pressure variations; and a metallic mesh sheath bonded onto and into said flexible boot for shielding said spherical shell from ambient electromagnetic interference.
 3. A hydrophone according to claim 2 further including: a preamplifier disposed in said flexible boot connected to said conductor means for amplifying and passing said representative signals to remote circuitry.
 4. A hydrophone according to claim 3 further including: a plurality of elastomers resiliently positioning said spherical shell in a spaced relationship from said flexible boot and said preamplifier preventing contact therebetween and the resultant generation of false signals.
 5. A hydrophone according to claim 4 further including: a coaxial cable reaching into said flexible boot connected to receive said representative signals and to pass them to remote circuitry.
 6. A hydrophone according to claim 5 in which said inner conductive means and said outer conductive means are metal films deposited on the inner and outer surfaces of said pair of hemispherical shells.
 7. A hydrophone according to claim 6 in which the inner conductive metal films define quadrature areas on each hemispherical shell and the outer conductive metal films define aligned quadrature areas creating eight said sections for serial interconnection creating increased omnidirectional sensitivity. 